Handbook EDU3 - V3.0_EN

Enrichment & Desorption Unit EDU3 EDU3
Handbook
Version 3.0
AIRSENSE Analytics GmbH AIR 16.10.2007

October 2007
The Enrichment & Desorption Unit EDU
Introduction
The EDU3 system has been designed for the co-operation with the Airsense Sensor Array Instrument PEN3. Volatile and semi volatile organic compounds in concentrations of less than the detection limit of an analytical instrument need to be enriched before analysis. Gaseous substances are trapped at sampling temperature (ambient) on adsorption tubes and forwarded to an analyzer after thermal desorption. The enrichment factor is related to many different physical and sampling parameters. It can be calculated on the basis of breakthrough volumes known from common tables. Typically, the detection limit can be reduced by a factor of 10 with volatile compounds and up to 1000 with low volatiles (e.g. limonene). Temperatures of the adsorbent material during sampling and desorption phases can be adjusted via settings within the software delivered with the instrument. Selective enrichment is possible by choosing suitable adsorbent materials. For example when analyzing beverages, highly volatile compounds, such as CO2 or even ethanol, are not enriched on the adsorbent "Tenax", while medium- or low-volatile substances, like most flavor compounds are trapped. Thus, the analysis can be limited to the actual flavor substances and the selectivity of the sampling device can be increased. With applications in very damp environments this hydrophobic polymer “Tenax” has also the advantage that cross influences of humidity on the analysis are avoided. The combination of heating samples and adsorption of the released compounds followed by desorption of the tubes is another option that can be very useful in some applications.
Principle of Operation
With the EDU the following analytical steps are performed automatically: 1) Sampling - time and temperature (elevated, if desired) can be adjusted 2) Postsampling - step for drying or extraction of undesired compounds 3) Desorption - bringing sample into the gas phase 4) Injection - transfer of sample to detector 5) Cleaning - tube conditioning by temperature increase 6) Cooling – cooling down until the sampling temperature is reached.
-1AIRSENSE Analytics GmbH Hagenower Str. 73 19061 Schwerin - Germany Registration no., HRB Nr. 4841 Schwerin tel: +49 385 3993 280 fax: +49 385 3993 281 email: info@ internet:

October 2007
The principle of operation is displayed in Fig. 1.
EDU
Desorption
Adsorption
Detector
Fig. 1 :
Principle of
operation of the EDU During the sampling step the compounds are trapped at ambient temperatures. The flow during sampling can be adjusted between 50ml/min and 500ml/min. The maximal sampling time depends on the retention volumes of the analyte on the adsorbent material. The standard trapping material delivered with the system is Tenax TA® (50/100mg)), but other adsorbent materials or combination of them are available upon request. After the sampling follows the postsampling step, in which Zero Gas from the port “Zero Gas1” will be passed through the tube in order to remove very volatile compounds from the adsorbent. After that, the tube is heated to its desorption temperature. There is no flow during the heating step. After heating the tube to temperatures T ≥ 160°C (Tmax=250°C) the gas flow is inverted and the trapped compounds are injected into the detector. inject Afterwards the tube is cleaned clean by heating to a higher temperature than the desorption temperature and the tube is rinsed with cleaned air. After cooling down to near ambient temperatures the trap is ready for the next measurement.
-2AIRSENSE Analytics GmbH Hagenower Str. 73 19061 Schwerin - Germany Registration no., HRB Nr. 4841 Schwerin tel: +49 385 3993 280 fax: +49 385 3993 281 email: info@ internet: